experiences using "options SCHED_ULE"

rosi rosi at encephalon.de
Fri Feb 13 00:16:11 PST 2004


hello,

i know ...

[/usr/srs/sys/conf/NOTES...]
# SCHED_ULE is a new experimental scheduler that has been designed for 
SMP, but will work just fine on UP too.  Users of this scheduler should 
expect some hicups and be prepaired to provide feedback.
[...]

... so here is the feedback.

We using FreeBSD 5.2.1 p2 on SMP machines (i386 / Dual-P3 / Dual-Xeon).
These servers running Apache+Suexec+PHP+Perl+Python and nfs(4).

We were curiously in the new scheduler and so we test it.

After building and installing the kernel (the only! thing that changed 
was "options SCHED_ULE") we see the system takes much more cpu time.

                            CPU time in %	
			usr	sys	idl
options SCHED_ULE	20-25    60-75    0-20
options SCHED_4BSD	30-35    35-40    0-35


Also we "see" much more suexec and php processes (usually, you can't see 
them because they are processed to fast ;) ) and the whole system felt 
slowly.

On the search for the reason why the machine takes so much cpu time for 
system, we found 400% to 500% more interrupts on the NIC's(fxp/em).

After building and installing a new kernel using SCHED_4BSD, the whole 
system runs like always. Very fast and well.

If it is necessary, i would post more informations.
But i think the "problem" is reproducibly on i386 SMP machines.

Naturally we will also test the SCHED_ULE again, if something changed.

---
Frank
rosi at encephalon.de


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